This project employs the methods of Drosophila cytogenetics and molecular biology to investigate the genetic basis of cellular differentiation. We have previously developed a method for the isolation and differentiation of embryonic myoblasts. We have investigated the necessary cell biology to establish this system as a reproducible and useful tool for further molecular investigations. The characteristics of RNA and protein synthesis during myogenesis have been investigated. Some myofibrillar proteins have been identified. These and some other proteins are synthesized only in myogenic cells and show increased synthesis associcated with the time of cell fusion. Cell free translation of mRNA extracted from myogenic cells indicates that the increased synthesis of myogenic proteins is related to transcriptional activity. We are presently using such mRNA in order to investigate gene location using in situ hybridization of such probes to polytene chromosomes.